Abstract The objective of this project is to develop a fluorescently-activatable reporter Chimeric Antigen Receptor T-cell (CAR-T) cell line for discovery of novel CAR-T receptors and their corresponding ligands. Significance: CAR-T therapy has demonstrated long-lasting treatment for hematological B cell malignancies but has yet to be effectively extended to other indications, e.g. solid tumors. Additional research tools are needed to expand the repertoire of available CAR-T therapies. Characterizing the performance of novel antigen/CAR-T combinations responsible for tumor clearance has proven to be a difficult challenge. We are developing a technology, PANACEA, that allows us to probe the behavior of a chimeric antigen receptor and its activation in a cellular context. Innovation: The core of the platform is an engineered cell line that contains an activatable synthetic reporter pathway. Upon CAR-T binding and cell activation, a reporter gene (e.g. a fluorescent protein) is expressed. This allows the researcher to detect activation events and use platforms such as cell sorting to isolate and study activated cells. By changing input parameters, PANACEA enables the study of variant libraries of CARs against single antigens, individual CARs vs libraries of antigens, or even full CAR-library-to-antigen-library screens. This reporter tool would enable rapid discovery and engineering of CAR-T constructs in a scientifically relevant context. Preliminary Data: We have constructed a novel cell line that fluorescently reports CAR activation with a library of inserted CARs and validated its ability to selectively trigger activation and find events as rare as 1:2000. Moreover, we have developed a suite of microfluidic platforms that allow for generation and cloning of paired heavy/light chain libraries into a CAR vector. Specific Aims: (1) Engineer the system components and assay conditions to increase assay activation while maintaining sensitivity in our model system (2) Demonstrate the platform?s performance against a suite of clinically-relevant targets (3) Use the system to screen a library of variant CARs against a known target.